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A continuation of the SAEFDE round-robin fatigue test program was conducted to determine the influence of a finer microstructure on monotonic tension, strain-controlled low cycle fatigue, fatigue crack growth, and fracture toughness of A356-T6 cast aluminum alloy. The finer microstructure castings, referred to as material W, were obtained using a water-chilled sand casting procedure. Material W exhibited more desirable ductile behavior than the previous SAEFDE materials X, Y, and Z. Material W exhibited superior smooth specimen low cycle fatigue resistance at both short and long lives, when compared to materials X, Y, and Z. This was due in part to the higher ductility and lower porosity of material W over materials X, Y, and Z. Material W exhibited similar fatigue crack growth behavior, and slightly higher values of fracture toughness at the same thickness when compared to materials X, Y, and Z.

Axial strain-controlled low cycle fatigue behavior was obtained from smooth specimens machined from spokes of A356-T6 cast aluminum alloy wheels. Two different foundries cast the wheels. Three wheels were used from one production run at one foundry and two wheels were used from two different production runs at the other foundry. Specimens from the three wheels of the same production run had essentially the same monotonic tensile properties and low cycle fatigue resistance. Specimens from the two wheels of the different production runs had different monotonic tensile properties and different low cycle fatigue resistance. All these A356-T6 wheel specimens cyclic strain harden with hysteresis loops typically offset to the compression side by five percent or less. The usual log-log linear model for low cycle fatigue adequately described the low cycle fatigue behavior.